Elevator landing monitor



y 1969 G. E. YEAKLEY 3,458,014

ELEVATOR LANDING MONITOR Filed Jan. 16, 1967 2 Sheets-Sheet 1 FIG.I

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y 9, 1969 G. E. YEAKLEY 3,453,014

ELEVATOR LANDING MON'ITOR Filed Jan. 16, 1967 M 882 SA 52 l 5A 32 582 g 1 M 8 fl'li 3 9 v Al gw .36

ELEVATOR STOP. 80

CONTROL E 8A2 F l% 2 Sheets-Sheet 2 FE uns FIG. 4A

FIG. 4

United States Patent 3,458,014 ELEVATOR LANDING MONITOR Glen E. Yeakley, Westfield, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 16, 1967, Ser. No. 609,480 Int. Cl. B66b 1/40 US. Cl. 187-29 13 Claims ABSTRACT OF THE DISCLOSURE This disclosure describes an apparatus for achieving more accurate landings in single-speed elevator systems where it is customary to cut off the power and apply the brake in advance of the intended stopping point so that the car drifts to a stop. Microswitches are utilized to determine whether the car came to rest above or below the intended stopping point. The microswitches through appropriate direction switches complete circuits to activate stepping switches which either increase or decrease the effective value of a variable resistor depending upon Whether the car undershot or overshot the intended landing point. The variable resistor is inserted in prior art circuits for cutting off the power and/or applying the brake so that the adjustment will result in less error on subsequent stops. The variable resistor is made up of a shunted resistor with numerous taps cOnnected to corresponding contacts on the two individually activated stepping switches. The system includes a relay which is activated when the effective value of the variable resistor is a minimum to open the circuit to the stepping switch which reduces the effective resistance so that the switches do not get out of sequence.

This invention relates to systems for controlling moving bodies, and it has particular relation to systems for bringing moving bodies, such as elevator cars, to accurate landings at a desired station or floor.

In systems for controlling moving bodies, such as hoists and elevator cars, it is desirable that the moving body be brought accurately to a stop adjacent any desired station or floor. For example, if an elevator car serves several floors of a building, it is desirable that control equipment he provided for bringing the car to a stop at any desired floor with the floor of the car and the associated floor of the building substantially in the same plane.

In many elevator systems, it is desirable to provide simple motive means which may include a polyphase induction motor. Such a motor has a'rate of rotation which varies as a function of the load connected to the motor. This means that the speed of an elevator car driven by such an induction motor varies as a function of the loading of the elevator car.

In order to stop an elevator car driven by such a single speed motor at a desired floor or station, it is conventional to cut off the power prior to reaching the level at which it is desired to stop the car and allow the car to drift into the landing. A mechanical brake is provided to reduce the amount of drift and to hold the car at rest. Since as mentioned above the speed of the car is dependent upon its loading, means must be provided for varying the stopping sequence so that accurate stops may be made regardless of load or direction or travel.

Various methods have been devised for taking into account variations in loading in an effort to achieve more accurate stops. One method is to vary the point at which the power is cut off and the brake is applied as does Patent No. 2,359,092. Alternatively the power can be cut off at the same point regardless of load but the time after power cutoff at which the brake is applied can be made 3,458,014 Patented July 29, 1969 variable. An example of this method can be found in Patent No. 2,403,125. Also, variable dynamic braking may be employed to provide the flexibility required for varying loads or may be used in conjunction with other variable means for adjusting the stopping distanceaswas proposed by Patent No. 2,669,324. Still another method is to vary the magnitude of the mechanical braking force as was disclosed by Patent No. 2,491,948.

All the above methods attempt to provide more accurate stops of single speed elevators by taking into account variations in loading. Unfortunately there are other factors which adversely affect the accuracy of the stop on an AC driven elevator, such as the temperature and condition of the brake lining and the brake wheel, and the condition of the gearing as well as other variable friction points. Therefore, although the systems which accommodate for variations in loading produce reasonably accurate stops they are not completely satisfactory because they do not take into account these other factors.

Accordingly, it is a general object of this invention to provide a new and improved single speed elevator system.

It is a more particular object of this invention to provide a new and improved single speed elevator system which accommodates for variations in the temperature and condition of the brake lining and the brake wheel, and the condition of the gearing as well as other variable friction points.

It is a further object of my invention to provide a means which accommodates for these factors which may be used in conjunction with any of the aforementioned methods which compensate for variations in loading.

Briefly, the present invention accomplishes the abovecited objects by providing a variable resistor the value of which is adjusted in accordance with the direction from which the car approached for the stop and whether the the prior stop was short of or beyond the desired stopping point.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of the specification.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

FIG. 1 is a schematic view of an elevator system embodying the invention;

FIG. 2 is a schematic view of a circuit diagram suitable for the elevator system of FIG. 1;

FIG. 2A is a key diagram which indicates the positions of the various relays and their contacts as shown in FIG. 2;

FIG. 3 is a schematic view of the invention used in conjunction with the power cutoff timer;

FIG. 3A is a key diagram which indicates the positions of the additional relays and their contacts appearing in FIG. 3;

FIG. 4 is a schematic view of the invention used as a time delay on a brake relay; and

FIG. 4A is a key diagram which indicates the position of the additional contacts of the relay appearing in FIG. 4.

In describing the specific embodiment of the invention as shown in FIGS. 1 and 2, reference will be made to the following apparatus:

Ddown relay HI-high microswitch LO-low microswitch 1 LSlong stepping coil Mcar running relay P-inductor plates OSovershoot relay SS-short stepping coil U-up relay Although the present invention may be adapted for use with any of the above methods for adjusting the stop according to load, for the sake of simplicity it will be described in conjunction with a system which varies the magnitude of the braking force in order to accommodate for variations in load. More particularly the invention will be described as being incorporated in the elevator system disclosed in Patent No. 2,491,948. Only those portions of the elevator system necessary for an understanding of the present invention will be described herein. For a fuller understanding of the overall operation of the system, reference should be made to the prior patent.

Referring to the drawings, FIG. 1 shows an elevator car 1 which is mounted for reciprocation in a vertical direction in a structure such as a building. Although the building may have a large number of floors, for the purpose of simplicity in presentation only one, floor 3, is illustrated in FIG. 1. It will be understood that a hatchway 5 extends through all floors of the building to per- .mit passage of the elevator car therethrough.

The elevator car 1 is secured to one end of the flexible cable 7 which passes over a sheave 9. The remaining end of the cable is secured to a suitable counterweight 11. The sheave 9 is secured to a shaft 13 for rotation therewith in a suitable bearing structure 15.

For the purpose of reciprocating the elevator car, motive means are provided which include a three-phase induction motor 17 having three phase windings 17a, 17b and 170. The rotor 17d of the induction motor is secured to the shaft 13.

In order to stop the elevator car, a brake wheel or drum 19 is secured to the shaft 13. This brake drum has associated therewith a brake shoe 21 which is biased against the drum 19 by means of a coil spring 23. Since the brake shoe 21 should be retracted from the drum 19 during normal running operation of the elevator, a solenoid B1 is provided which has a magnetic core 25 secured to the brake shoe 21. When the solenoid B1 is energized, the brake shoe 21 is retracted from the drum 19 against the force exerted by spring 23.

Movement of the elevator car 1 is controlled by a car switch CS found in the elevator car. In addition, the elevator car carries an inductor or floor-stopping relay S which is positioned to pass inductor plates UP and DP during reciprocation of the elevator car in its hatchway. The inductor plate DP is for the purpose of controlling the stopping of the elevator car 1 as the car descends toward the floor 3. The inductor plate UP is for the purpose of controlling the stopping of the elevator car as it ascends toward the floor 3. It will be understood that a similar pair of inductor plates are provided for each of the floors served by the elevator car. The portions of FIG. 1 thus far specifically described are wellknown in the art, and a detailed discussion thereof is believed to be unnecessary.

Normally opened mechanical switches designated HI and LO are attached to the elevator car and are operated by cams 71 and 72 respectively fastened to the walls of the hatchway in the vicinity of each of the landings. When the car comes to a stop either above or below the desired stopping point, the appropriate switch is closed by its corresponding cam. The cam plates can be located so as to indicate an error of as little as /1 of an inch if desired.

As previously pointed out, the drift of the car 1, after the spring 23 has applied the brake shoe 21 to the drum 19, depends on the loading of the car. To compensate for variations of such loading, a generator 27 has its rotor secured to the shaft 13. Although an alternating-current generator may be employed, it will be assumed for the purpose of discussion that the generator 27 is a directcurrent generator having a separately excited field winding F. It will be understood that the output voltage of the generator 27 varies as a. function of the load on the elevator car 1 since as mentioned previously the rate of rotation of a polyphase induction motor is dependent upon load. The output voltage is connected through contacts T1 of a suitable relay and variable resistors 29 and 60 to a solenoid B2. This solenoid has a magnetic core 31 connected to the brake shoe 21. Energization of the solenoid B2 increases the braking effort developed by the brake shoe 21 and the drum 19in accordance with a function of the load carried by the elevator car 1, and, by the addition of the present invention, with a function of the other variables present such as temperature and condition of the brake lining and other moving parts.

'Accommodation for the latter function is achieved by adjusting the variable resistor 60. By analyzing each stop to determine whether the car came to rest either above or below the desired stopping point, it can be determined whether the value of resistor 60 should be increased or decreased. Since the generator 27 is assumed to be making reasonably correct adjustments for variation in loading, any error in the stopping position can be assumed to be attributable to a change in temperature of the brake drum, the condition of the brake drum, etc. Unlike the loading which can change appreciably between movements of the car, the other factors change more slowly, but if permitted to accumulate they could account for troublesome error.

The determination as to whether the efiective value of the resistor 60 should be increased or decreased depends upon two factors: (1) whether the car is stopped above or below the desired stopping point, and (2) whether the car had been traveling in the up or down direction.

Assume that a car traveling in an up direction comes to rest below the level of the floor. This car has stopped short of the intended landing point and the braking force should be reduced so that the next time the car comes to a stop it will coast a little farther. In order to reduce the braking force the effective value of resistor 60 should be increased. This will reduce the current of the brake coil B2 and in turn reduce the braking force applied to the brake drum. On the other hand, if a car had been traveling down and had come to rest below the desired stopping point the braking force should be increased. This can be accomplished by reducing the effective value of the resistor 60.

The effective value of the resistor 60 in series with the brake coil B2 is varied by the two stepping switches and 81. The corresponding contacts of the two stepping switches are connected to the same point on resistor 60. These stepping switches are a conventional type with double wiper arms and in this arrangement each switch is provided with two rows of contacts a and b. The switches are stepped independently in the directions of the arrows by the stepping coils SS and LS respectively. Since the wiper arms of 80 are ahead of the wiper arms of 81, stepping of stepping switch 80 increases the effective resistance in the brake circuit. Conversely, stepping of stepping switch 81 tends to reduce the elfective resistance in the brake circuit. Means are provided, and will be described below, to prevent the wiper arm of switch 81 from passing up the wiper arm of switch 80. The wire 61 joining the two ends of the resistor 60 is provided so that the stepping switches may be continuously stepped in the directions of the arrows without interrupting the continuity of operation. To illustrate, assume that the stepping switch 80 has stepped in the direction of the arrow until its wiper arm X, has come in contact with contact C while the stepping switch 81 is stepped in the direction of the arrow until its wiper arm X, has come into contact with contact C as shown by the dotted lines in FIG. 1. In this configuration the effective resistance of resistor 60 in the brake coil circuit is the resistance between P and P This is assuming that the resistance high that it can be ignored for present purposes. If it is now determined after the next stop that the braking force should be reduced i.e. the effective resistance of resistor 60 should be increased, stepping switch 80 will step one more step in the direction of the arrow so that wiper arm Y will come into contact with contact C and wiper arm X, will become ineffective. The effective resistance of resistor 60 has now been increased one more unit by the addition of the resistance between P and P If three more demands for a reduction in the effective resistance are made, then stepping switch 81 will move in the direction of the arrow until wiper arm Y becomes effective. As demands are made for changes in the effective resistance the appropriate stepping switch will be advanced always in the direction of the arrows. By the proper choice of parameters, stepping switch 80 should never advance more than a few steps ahead of stepping switch 81. In this manner stepping of stepping switch 80 in the direction of the arrow will assure that the effective resistance of resistor 60 will be increased for each advance. On the other hand, if 80 is permitted to get so far ahead of 81 that the portion of the resistor 60 between wiper X moving to the right to wiper X equals more than one half of the total value of the resistor 60 then the next step of stepping switch 80 would actually reduce the effective resistance of 60 presented to the brake coil cir cuit because the portion of the resistor 60 in parallel would be reduced and would be less than resistance between X,,' and X,, moving in the direction of the arrow. This would cause the car to stop even shorter the next time which would again initiate a demand for less braking force and therefore more resistance. Again stepping switch 80 would move in the direction of the arrow thus further reducing the effective resistance. The result would be that stepping switch 80 would continue to cycle after each stop. As mentioned, this could be avoided by a proper choice of parameters or it could be prevented by mechanical means such as a lost motion coupling to prevent wiper X, from getting too far ahead of X,,'.

For an understanding of the derivation of the signals which activate the stepping switches 80 and 81, a brief description of the operation of the overall system is in order. Referring to the control circuit illustrated in FIG. 2, it will be observed that a source of three phase electrical energy is represented by three phase conductors A, B and C. Two of the phase conductors A and C are connected through a full wave rectifier 53 which may include a filter, if desired, to provide a direct-current voltage between the ouptut conductors L1 and L3. The various relays are energized by direct-current supply from these conductors L1 and L3.

With the car switch CS in the neutral position indicated in FIG. 2, a circuit is established for energizing the floor-stopping relay S and an auxiliary stopping relay T which controls the previously mentioned contacts T1. When the car switch CS is rotated in a clockwise direction, as viewed in FIG. 2, to engage a contact CS1, an energizing circuit is established for the down relay D and the car-running relay M. Energization of the down relay D results in closure of the front contacts D3 of the relay .D to establish a holding circuit for the relays D and M. This holding circuit may be traced from the conductor L1 through the relays M and D, front contacts D3 and back contacts S1 of the floor-stopping relay S. Energization of the relay M also results in closure of the front contacts M1, M2 and M3, which respectively connect phase conductors A, B and C to the induction motor 17. Front contacts D1 and D2 of the down relay D also are closed by energization of the relay D. These contacts D1 and D2 complete an energization circuit for the three phase motor 17 which conditions the motor to move the elevator car 1 of FIG. 1 in a downward direction.

At the same time, closure of the front contacts M4 by energization of the car-running relay M and closure of the front contact D4 of the relay D, completes an energizing circuit for the solenoid B1. Energization of the solenoid B1 releases the brake shoe 21 from the drum 19 to permit the desired movement of the elevator car. Consequently, the car 1 moves in a downward direction. It will be noted that the required movement of the car switch CS into engagement with the contact CS1, for the purpose of initiating downward movement of the elevator car, results in deenergization of the relays S and T.

Energization of the car-running relay M also closes the front contacts M5 thereof to energize a field winding F of the generator 27. However, since the contacts T1 are open, the voltage output of the generator is not applied to the solenoid B2. At the same time back contacts M6 of the running relay are opened thereby precluding adjustment of the variable resistor 60 while the car is in motion. These contacts are provided with a dashpot or other type of time delay providing a delay of suitable duration so that the car will come to a complete stop after deenergization of the car running relay before its contacts M6 will again close.

Let it be assumed that with the elevator car conditioned for movement in a downward direction, it is desired to stop the elevator car at the floor three. Such stopping is initiated by centering the car switch CS to engage the contact CS3. The movement of the car switch energizes the relays S and T. Energization of the auxiliary stopping relay T closes its front contacts T1, but the resulting energization of the solenoid B2 is ineffective for the reason that the solenoid B1, which develops an appreciably stronger force, is still energized. Since the floor-stopping relay S is of the inductor type, energization of its winding does not affect the relay contacts until the floor-stopping relay reaches the down inductor plate DP. At such time, the back contacts S1 open to deenergize the down relay D and the car-running relay M. The resulting opening of the contacts M1, M2, M3, D1 and D2 deenergizes the induction motor 17.

The deenergization of the down relay D and the carrunning relay M also opens the front contacts D4 and M4 to deenergize the solenoid B1. The rate of the deenergization of the solenoid is determined by a discharge resistor 55 connected across the terminals of the solenoid. Deenergization of the solenoid B1 permits the spring 23 to urge the brake shoe 21 against the drum 19. Furthermore, since the solenoid B1 is deenergized, the solenoid B2 now is effective for increasing the braking effort developed by the brake shoe 21 and the brake drum 19 in accordance with the voltage output of the generator 27, as affected by the variable resistor 60. The elevator car now drifts until the floor of the elevator car 1 and the floor 3 are substantially in the same plane. Since the output of the generator 27 compensates for variations in the loading of the elevator car 1 and the variable resistor 60 compensates for variations in such factors as temperature and brake condition, the elevator car is landed accurately at the floor 3 despite substantial variations in these factors. The front contacts MS of the carrunning relay are provided with a time delay in opening, sufficient to insure energization of the field winding F until the elevator car is completely stopped.

After the car has come to a complete stopaccuracy of the stop is analyzed to see whether variations in temperature or brake condition necessitate adjustment of the effective value of the resistor 60. As mentioned previously the back contacts M6 of the car-running relay M are equipped with a suitable time delay to assure that the car has come to a complete stop before the analyzing circuit is energized. Also it should be recalled that in analyzing the accuracy of the stop it is necessary to know whether the car has been traveling in the up or down direction. Since the up relay U and the down relay D in the elevator system illustrated in FIG. 4 are deenergized by the appropriate inductor plate prior to reaching the desired floor it is necessary to provide contacts of these relays with time delay mechanisms. Therefore the contacts U5, U6, D and D6 are provided with suitable time delay mechanisms so that these contacts will remain closed despite deenergization of the coils for a period sufficiently long after the contact M6 closes to permit any required adjustment of the elfective resistance of the resistor 60.

Assume now that in this downward trip of the elevator, the car came to rest a couple of inches above the plane of the third floor. When the inductor relay S passes the down in inductor plate DP, relay D deenergizes. However, the delay mechanism mentioned above maintains contact D5 in a closed position. As the car 1 approaches the third floor from above, the cam 71 on the wall of the hatchway closes the HI switch. This contact will remain closed even after the car has come to rest because the car stopped above the intended stopping point. Since the car stopped high and was traveling in a down direction, it stopped short of its intended landing point. When the car has come to rest and the time delay on the contact M6 has timed out permitting the contact to close, the circuit is completed for stepping the short stepping switch 80 by activation of the short stepping coil SS. This circuit is as follows:

L1, HI, D5, SS, M6, L3

Suppose however, the elevator car drifts beyond its intended landing point so that it comes to rest at a position where the cam 72 in the hoistway closes the LO switch. This stop is long and it is desirable to advance the stepping switch 81 so as to reduce the effective resistance of resistor 60 thereby increasing the braking force for the next stop. When the M6 contacts close the following circuit is completed thereby advancing the stepping switch 81 one notch:

L1, L0, D6, LS, 051, M6, L3

Contact 051 is a back contact of the overshoot relay. Since the designed function of the long stepping switch is to reduce the efiective resistance of resistor 60, it is desirable to provide means for preventing the stepping switch 8-1 from passing up the stepping switch 80 because once it has, further advancement will increase rather than decrease the effective resistance of resistor 60. Of course the parameters of the system should be chosen so that this condition never arises, however, if less than the minimum effective value of resistor 60 is called for, the overshoot relay will prevent stepping switch 81 from passing up stepping switch 80. This is accomplished by providing a relay which will be operated when the current through its coil reaches the magnitude of the current drawn by the combination of the coil and the minimum value of the efiective resistance of 60 connected in series. The effective value of the resistor 60 as seen by the brake circuit is introduced in series with the relay OS by utilizing another row of contacts on each of the stepping switches (80 81 and connecting the corresponding contacts of these switches to corresponding points on 'a resistor 62 which is identical to resistor 60 and is shunted by the wire 63. Thus, the following circuit is completed for the overshoot relay:

L1, OS, 81 62, 80 L3 Since the wiper arms X; and X, of 81 are mechanically connected together as are the wiper arms X,, and X, of switch 80, when the wiper arm X advances to the contact corresponding to the contact which wiper arm X is at so that the minimum effective resistance of resistor 60 is presented to the braking circuit, wiper arms X and X;, are likewise opposite corresponding contacts and therefore the minimum effective resistance of resistor 62 permits sufiicient current to flow through OS to operate that relay. This opens the contact 081 thus preventing the stepping switch 81 from being advanced until stepping switch 80 has been advanced. The relay OS is faster acting than the long stepping coil so that 0S1 opens before LS has a chance to operate. Alternatively, stepping switch 81 could be prevented from passing up stepping switch by mechanical means such as by equipping the wiper X, with an arm which would push wiper X along with it when it attempted to pass X or by utilizing a lost motion coupling on wiper X,,'.

If the car had been traveling in the up direction and was low, the stop was short. Under these conditions contact U6 would be closed and the stepping switch 80 would be advanced by the short stepping coil SS. Conversely, if an upward traveling car stopped high the stepping switch 81 should be advanced by the long stepping coil LS. Contact U5 provides the proper switching for this.

Although the invention has been described in detail as a component part of an elevator system which varies the magnitude of the braking force to accommodate for variations in stopping distance, the invention could be adapted for use with any of the other previously mentioned methods of accommodating for variations in loading. For instance, the variable resistor 60 could be inserted in a charging circuit of a power cutotf timer which varies the point at which the power to the motor is cutoff as a function of the load.

In a well-known type of timer, the rate of charging of a capacitor determines the time it will take for the voltage across the capacitor to reach sufiicient magnitude to operate an electronic switch. In an elevator system, if the charging current is made dependent upon the load, the time for cutting oil the power can be varied accordingly. In addition, since the firing time of such a timer can be varied by adjusting the value of a resistor in series with the capacitor, my invention could be employed to enable such a system to respond to variations in the operating conditions of the moving parts by placing the variable resistor 60 in series with the capacitor of the timer as shown in FIG. 3.

In the apparatus of FIG. 3, the elevator stop control produces a constant output except when the electronic switch within thecontrol is activated. This switch is activated when the voltage across the capacitor C, reaches a predetermined value. The time when this occurs is dependent upon the rate at which the capacitor C charges which in turn is controlled by the current limiting'resistors 60 and 64. Resistor 60 is identical to resistor 60 of FIG. 2 and its value is similarly adjusted by stepping switches 80 and 81. The value of resistor 64 is adjusted in accordance with any of the prior art methods of compensating for variations in loading,

When the elevator car is at rest, the auxiliary relay SA is activated through the following circuit:

L1, SB2, SA, S2, L3

Where the contacts SB2 are back contacts of the auxiliary relay SB which is deenergized by the make contacts M of the running relay M, and the contacts S2 are back contacts on the inductor relay S. With SA energized the holding contacts SAl are closed and the break contacts SA2 are opened to remove the charging current from the capacitor C At the same time, the make contacts SA3 are closed to insure that the voltage across capacitor C is reduced to zero through resistor 65 prior to the initia- When the switch CS is rotated counterclockwise to start the car in the up direction, relays M and U are energized. Energization of relay M opens contacts M and M and closes the M contacts. The closing of the latter contacts permits the elevator stop control to energize relay SB. The make contacts SBl along with the contacts U3 then complete a holding circuit for the M and U relays. The break contacts SE2 of relay SB open, but the relay SA is held in by its holding contacts SAl.

When it is desired to stop at the next floor, the switch CS is centered thus energizing the inductor relay S. The car continues to run because relays M and U are held in by U3 and 881. When the relay S passes the inductor plate associated with the floor at which the car is to stop, the contacts S2 are opened deener izin the SA relav.

The contacts SA3 open removing the shunt circuit around capacitor C and the contacts SA2 close completing the charging circuit as follows:

L1, SA2, C 64, 60, L3

Capacitor C charges at a rate dependent upon the time constant of this series combination. Since the value of resistor 64 is set in accordance with the load being hauled and the value of resistor 60 is set, according to this invention, to accommodate for variations in the operating conditions of the moving parts of the system, the time for power cutoff is appropriately delayed. When the voltage across capacitor C reaches sufiicient magnitude to a'ctivate the elevator stop control, relay SE is deenergized. Contacts SBl open deenergizing relays U and M and thereby cutting off the power to the motor and applying the brake. Contacts SBZ close and through the contacts S2, which reclosed after the car passed the inductor plate, the relay SA is reenergized. Contacts SA2 then open the charging circuit while contacts SA3 close to shunt capacitOl' C1.

The M contact is provided with a time delay similar to that utilized on contact M in FIG. 2 so that the analyzing circuit which functions identically to that in FIG. 2 is not activated until the car has come to a complete stop. If the up traveling car then came to rest above the intended stopping point, stepping coil LS would be activated which would advance the stepping switch 81 in the direction of the arrow thus reducing the elfective value of the resistor 60. Less resistance in the charging circuit of C would mean that on the next stop the power would be cut oil sooner thus compensating for the stopping error.

In the configuration of FIG. 3, the overshoot relay OS is introduced directly into series with the resistor 60 when the contact M is closed. This contact has a time delay associated with it of the same duration as that on M so that it does not close until after the car has come to rest. As in the apparatus of FIG. 2, if the wipers of stepping switches 80 and 81 are opposite corresponding contacts so that the effective resistance of resistor 60 is at a minimum, the current through OS will be sufficient to activate that relay. This in turn will open contacts 081 and prevent stepping switch 81 from passing up stepping switch 80.

Hence the invention can be employed to vary the time of power cut-01f to accommodate for variation in the operating condition of the moving parts of an elevator system.

In addition, it is possible to adapt the invention so that the elfective resistance of resistor 60 would be reduced if an upward traveling car stopped low. Such an adaptation could be useful where the resistor 60 was shunted around the brake coil to delay application of the brake after power to the brake coil is removed as shown in FIG. 4. In such an arrangement, the greater the shunt resistance the sooner the energy stored in the coil will be dissipated. Therefore if the car was short it is desirable to reduce the effective value of the resistor 60 so that upon the next stop the application of the brake will be delayed somewhat. Only minor adjustments of the apparatus need be made to achieve this. All that is necessary is to connect the short stepping coil SS to stepping switch 81 rather than to stepping switch 80, The contact 081 of overshoot relay OS should be connected in series with the coil S as shown in FIG. 4 rather than the coil LS since the latter should now be connected to stepping switch 80. Now when the car stops beyond the desired stopping point the etfective resistance will be increased.

The apparatus of FIG. 4 is also arranged so that the overshoot relay OS is operated directly by the effective resistance of resistor 60. When either the up or down relay is energized, the brake relay B is actuated to release the brake either through contact U; or D respectively. At the same time, the car-running relay M is activated thus closing contacts M and M and opening contacts M M and M Assume that the car is conditioned for up travel so that contact U is closed. When the appropriate circuits (not shown) are completed to deenergize the relay, the contact U, is opened thus cutting olf power to the brake relay B. Contacts M M and M are provided with time delays similar to the type used on contact M of FIG. 2 so that these contacts remain open until after the car has come to a complete stop. Contacts M and M are provided with time delays which keep them closed after the relay M is deenergized for a period of time just slightly shorter than the delay on the M M and M contacts, so that the resistor 60 is shunted across the brake coil during the stopping sequence. After the car has come to rest, the contacts M and M open. Then the contacts M and M close, and if the wiper arms of stepping switches and 81 are positioned at corresponding contacts the current through OS will be sufficient to activate the overshoot relay thus preventing activation of the short stepping coil SS. It will be understood that the relay OS is faster acting than coil SS.

To summarize, this invention monitors each stop of the elevator to determine whether the car stopped short of or beyond an intended landing point and feeds corrective information into the stopping sequence. Since this invention is used in conjunction with means adjusting the stopping sequence for variations in loading of the car, the corrections made by it are for variations in the operating conditions of the moving parts. Since the latter variables change only slightly from trip to trip, it is only occasionally that a one step adjustment in either direction is necessary.

While this invention is adaptable for use with many systems for controlling moving bodies, it is particularly adaptable for providing accurate stops in single speed elevator systems. It can also be utilized in two speed elevator systems Where leveling is normally provided to obtain accurate stopping. With this invention, the leveling devices and circuitry would no longer be required since level landings would be virtually assured with a substantial saving in hardware. Although the invention was particularly described for use with an attendant operated elevator system, this was done solely for ease of presentation and the invention is equally adaptable for use with an automatic system.

I claim as my invention:

1. In a system for controlling a movable body, a structure, a body movable relative to said structure, motive means for moving said body relative to the structure, control means for stopping said body at predetermined stations relative to the structure including means analyzing whether the body was stopped short of or beyond a selected station and adjusting said stopping means to assure less error on subsequent stops.

2. The system of claim 1 in which said means for determining whether the body was stopped short of or beyond the selected point at which the body was to come to rest comprises means responsive to the direction of travel of said body and means responsive to whether the body came to rest to one side or the other of the selected stopping point relative to said structure.

3. The system of claim 1 wherein said adjusting means comprises a variable impedance the value of which is varied step-wise by two stepping switches, one of which reduces the effective impedance in response to a first signal from said analyzing means, the second of which increases the effective impedance in response to a second signal from said analyzing means.

4. the system of claim 3 in which said first signal is delivered by said analyzing means if said body is stopped beyond the intended stopping point and in which said second signal is delivered if the body is stopped short.

5. The system of claim 3 in which the impedance is a continuous resistor and in which said stepping switches tap said resistor at discrete points as they are individually ping switch following behind the Wiper of the second.

6. The system of claim in which means prevent the wiper of said first stepping switch from passing up the wiper of said second stepping switch.

7. The system of claim 6 in which the means preventing the first stepping switch from passing up the second comprises a current activated switch which blocks further signals to the first switch when the current through said current activated switch which is a function of the efiective resistance of the variable resistor reaches a value corresponding to the minimum effective resistance.

8. The system of claim 6 in which means preventing said first stepping switch from passing up the second comprises a current activated switch, a second bank of contacts on each stepping switch and a second continuous resistor similarly tapped by said second bank of contacts so connected that when the second wipers of the second bank of contacts which move in step with the first wipers are opposite corresponding contacts the current through the circuit will be sufiicient to activate the current activated switch which in turn blocks the first stepping switch from receiving said first signals until the second stepping switch has again been stepped.

9. The system of claim 1 including means preventing adjustment of'said stopping means when the body is not at rest. s

10. The system of claim 1 in which said means for stopping said body at predetermined stations relative to the structure include means responsive to variations in the load being transported.

11. In an elevator system, a hoistway, stations spaced vertically in said hoistway to be served by an elevator car, an elevator car, means for reciprocating said car vertically within said hoistway, and stopping means for bringing the car to a stop opposite said stations including means analyzing whether the body was stopped below or above a selected station and adjusting said stopping means to assure less error on subsequent stops.

12. The elevator system of claim 11 in which the analyzing means comprises means mounted in said hatchway above and below the desired stopping points for activating sensors mounted on said elevator car and means responsive to the directions from which the car approached for the stop.

13. The elevator system of claim 11 in which said stopping means for bringing the car to a stop opposite said stations includes means responsive to variations in the loading of the car.

References Cited UNITED STATES PATENTS 2,359,092 9/ 1944 Eames et al 187--29 2,491.948 12/1949 BeI'kOVitZ 187-29 2,669, 24 2/1954 Lund 18729 ORIS L. RADER, Primary Examiner W. E. DUNCANSON, 111., Assistant Examiner US. Cl. X.R. 318-372 V 

